Balloon catheter for rechanneling stenoses in body passages, in particular of coronary and peripheral arterial vessels

ABSTRACT

A balloon catheter for rechanneling stenoses in body passages, in particular of coronary and peripheral arterial vessels, has a microwave antenna provided in the interior of the balloon, which antenna is connected to a microwave generator by way of a coaxial cable. By action of the microwaves on a microwave-absorbing dilatation liquid and/or a metallic coating on the envelope of the balloon, the catheter is heated and the vessel wall is subjected to thermal aftertreatment to prevent restenosis.

BACKGROUND OF THE INVENTION

The invention relates to a balloon catheter for rechanneling stenoses inbody passages, in particular of coronary and peripheral arterialvessels, with a balloon through which a guide hose guided by a guidewire extends and which is inflatable with a gas or liquid by way of aninflation tube opening into the interior of the balloon.

Balloon catheters for rechanneling stenoses in coronary vessels havebeen in use by cardiologists for some time, restenosis in 35% ofapplications being problematic as the chief late complication of theclinically very successful technique. For this reason, it has beenproposed to use laser light for thermal aftertreatment of a balloondilatation with the aid of a light wave guide (The American Journal ofCardiology 56, 953).

European Patent A 2,182,689 describes a balloon catheter for which thetissue surrounding the balloon is heated with laser light fed into theballoon. From the same source, it is known also that an electric heatingelement may be provided near the distal end of the guide wire, theelement being enclosed by the balloon and heating the fluid present inthe balloon. The guide hose extending through the balloon is of adiameter only slightly greater than the diameter of the guide wire toavoid the hazard of coagulation of blood penetrating into the guidehose.

From Biomedizinische Technik 32, September 1987 supplement, 33-36, it isknown that high-frequency energy may be used to support balloondilatation. Thus it is proposed that the balloon catheter be providedwith a bipolar electrode configuration of two strip electrodes. Thestrip electrodes are connected to a generator with a frequency of 0.5 to1 MHz for a period of up to 38 seconds and an output energy of 50 wattsmaximum. With high-frequency coagulation in the region of the stripelectrodes, animal experiments are to ascertain whether a stabilizeddilatation can be achieved.

Another device for thermal treatment of the tissue surrounding bodycavities with temperature control means is described in U.S. Pat. No.4,658,836, a direct heating of the body tissue being effected byelectromagnetic radiation in the frequency range of radio waves ormicrowaves.

German Patent 3,011,322 discloses a radiation probe for a device formicrowave treatment of body tissue, at the same time permittingapplication of hyperthermia and radiotherapy, the tissue beingirradiated with microwave energy. To concentrate the microwave radiationon the desired tissular region, the radiation probe, capable of beingintroduced into a body cavity, is fitted out with a coaxial cable whoseunshielded end is asymmetrically surrounded in the probe by a bulbousbody.

U.S. Pat. No. 4,662,383 describes a balloon catheter for hyperthermia oftumors, charged by way of a supply line with a coolant capable of beingdrained from the interior of the balloon by way of an outlet line. Inthe interior of the balloon, a microwave antenna is provided, having arange of radiation extending into the surrounding tissue. Fluids havinga low absorption coefficient for microwaves are provided as coolants, inorder not to impede penetration of the microwave into the tissue.

SUMMARY OF THE INVENTION

Against the background of the prior art outlined above, the object ofthe invention is to create a balloon catheter permitting conservativehomogeneous heat therapy with a variable and suitably controllablethermal depth of penetration.

In a balloon catheter of the kind mentioned at the outset, this objectis accomplished, according to the invention, in that a microwave antennacapable of being connected to a microwave generator by way of a coaxialcable is arranged in the interior of the balloon.

The microwave antenna in the interior of the balloon serves primarily toheat the fluid used to dilate the balloon envelope, said fluidcomprising a good liquid absorbent for microwaves, for example a mixtureof a common salt solution and a contrast medium containing iodine, towhich other substances may be added if desired to enhance the microwaveabsorption, as for example metal particles suspended in the liquid. Theradially symmetrical propagation of the microwaves leads to ahomogeneous radially symmetrical heating of the liquid.

To prevent direct penetration of microwaves into the tissue surroundingthe balloon catheter, the balloon envelope is preferably provided with ametallic coating. To prevent blood present in the guide hose thattraverses the balloon envelope from coagulating when the microwavegenerator is switched on, the guide hose is capable of being squeezedflat by the pressure of the fluid used for dilatation, so that in suchan embodiment the guide hose need not be metalized for shielding, whichwould interfere with a uniform distribution of microwave energy in theinterior of the balloon.

In an expedient embodiment of the invention by way of example, themicrowave antenna consists of the anterior end, stripped of itsshielding, of a coaxial cable. The arrangement is such that the metallicinner conductor extends along the lengthwise centerline of the inflatedballoon, to permit a uniform distance from the balloon wall and hence auniform thermal treatment.

DETAILED DESCRIPTION OF THE INVENTION

In the following, an embodiment of the invention will be described byway of example with reference to the drawings. In the drawings,

FIG. 1 shows a balloon catheter according to the invention in lengthwisesection,

FIG. 2 shows a balloon catheter according to the invention in inflatedcondition, partly in section and partly in cut-away perspective, and

FIG. 3 shows a cross-section through the midregion of the inflatedballoon envelope of the balloon catheter.

In FIG. 1, the balloon catheter for rechanneling stenoses in coronaryvessels is represented in lengthwise section. The balloon catheter has aballoon comprising an envelope 1 consisting of a flexible heat-resistantplastic. The envelope 1 is provided on the outside and/or inside with ametallic coating not identified in the drawing. The metallic coating ofthe balloon consists preferably of a film of gold, silver, chromium,chrome-nickel or copper. The coating may be of uniform thicknessthroughout, or a fine network with interruptions, for example in theform of stripes. The coating serves to shield against microwavesgenerated in the envelope 1 to the outside, and as a heating surfaceheated by microwave absorption.

The envelope 1 encloses a flexibly compressible guide hose 2, which,depending on the construction of the balloon catheter, is only slightlylonger than the envelope. The guide hose 2 serves to guide the ballooncatheter along a guide wire 3 advanced into the field of operation.

To inflate the envelope 1 with a fluid forced into the interior 4 of theenvelope 1, an inflation tube 5 is provided, shown dotted in FIG. 1 andin partial perspective in FIG. 2. The inflation tube 5 has orifices 6 atits anterior end, through which communication is set up between theinterior of the inflation tube 5 and the interior 4 of the envelope 1,so that the liquid can be forced into the interior 4 of the envelope 1as indicated by arrows 7.

When the envelope 1 of the balloon catheter is located in the region ofa stenosis to be rechanneled in a coronary vessel of the patient, theguide wire 3 is retracted more or less to the position seen in FIG. 2.

As may be seen in FIG. 2, the guide hose is long enough at the end tothe left in FIGS. 1 and 2 to prevent the guide wire 3 from escaping outof engagement with the guide hose 2 when retracted.

When the interior 4 of the envelope 1 is charged with liquid underpressure as shown in FIGS. 2 and 3, the guide hose 2 is squeezed flat bythe internal pressure in the manner indicated in the envelope 1 in FIGS.2 and 3, with the result that no heat-coagulated blood will pass throughthe guide hose 2 in the direction towards the retracted guide wire 3.

Above the guide hose 2 and inflation tube 5 in FIGS. 1, 2 and 3, acoaxial cable 8 is seen. The metallic inner conductor 9 of the coaxialcable 8 extends along the centerline 10 drawn in FIGS. 1 and 2 into thevicinity of the envelope 1, but leaving a distance between the anteriorend of the inner conductor 9 shown at the right in FIGS. 1 and 2 and theinflated envelope 1.

The inner conductor 9 of the coaxial cable 8 is sheathed with insulation11, likewise electrically insulating the anterior end 12 of the innerconductor 9 from the liquid for example present in the interior 4.

The shielding 13 of the coaxial cable 8 extends by an amount more orless matching the distance of the anterior end 12 of the metallic innerconductor 9 from the envelope 1 into the interior 4 of the envelope 1.As usual for coaxial cables, the shielding 13 of the coaxial cable 8 isenclosed by an outer protective jacket 14. The coaxial cable 8 extendstogether with the guide wire 3 and the inflation tube 5 through a guidecatheter not shown in the drawing, terminating for example in theinguinal region of the patient's body, to a microwave generator with afrequency in the range from 400 MHz to 10 GHz. The output power and theon-times of the microwave generator are preadjustable, a pressure switchnot shown in the drawing preferably sensing the internal pressure in theenvelope 1 in order to permit the microwave generator to be switched ononly at a dilatation pressure at which the guide tube 2 is squeezedflat, thus securely avoiding any coagulation of blood by the microwavesin the guide hose 2. Specifically, the microwave generator may be soconstructed that the high-frequency output is made available pulsewise,the pulse test ratio and the duration of a pulse train beingpreadjustable according to the prevailing conditions of operation.

When the envelope 1 has taken on the more or less cylindrical shaperepresented in FIGS. 2 and 3 and the inner conductor 9 lies along thecenterline of the vessel to be dilated, the microwave generator isswitched on and the liquid is heated as a heat reservoir around theinner conductor 9 acting as antenna and then the inner vessel wall isheated by conduction to perform a thermal aftertreatment of themechanically dilated vessel wall, in particular a vessel wallcoagulation, thus reducing the tension set up in the vessel wall and/orcoagulating any existing lesions. The heating of the liquid isaccomplished by absorption of microwave energy. To increase absorption,it is expedient for the liquid used to be a common salt solution thatmay be mixed with an X-ray contrast medium containing iodine. Inaddition, metal particles or other substances absorbing microwaves maybe mixed in.

The zone of thermal influence may be adapted to prevailing conditions bychoice of liquid medium and the frequency, power and pulse shape of themicrowaves. Adaptation is possible also by means of the aforementionedmetallic coating on the envelope 1. Depending on choice of liquid andform of coating, the latter may merely shield the envelope 1 or beitself heated and give off its own heat or heat transferred from theliquid to the surroundings by conduction.

After the thermal treatment, the envelope 1 is decompressed and theballoon catheter is retracted together with the guide wire 3.

Retraction of the guide wire 3 before the microwave generator isswitched off also has the result that the microwave output emerging inthe unshielded region of the inner conductor 9 will not be shielded bythe guide wire 3, and in particular the guide wire 3 will not be heated.

The envelope 1 is welded to the guide hose 2 at the end on the right inFIGS. 1 and 2. At the posterior end, shown on the left in FIGS. 1 and 2,the envelope 1 is welded tight to the guide hose 2 and the outer jacket14 of the coaxial cable 8.

In the balloon catheter to be heated with microwaves as described above,energy is introduced into the balloon and there converted into heat inthe liquid and/or the coating of the envelope without passing a currentthrough the body of the patient and without presence of a galvanicallyclosed circuit.

The balloon catheter may be employed to especial advantage in coronaryvessels. Alternatively, however, with suitably enlarged diameter, it maybe used to dilate other arterial vessels as well as any body passagesand cavities.

I claim:
 1. A balloon catheter for rechanneling stenoses in bodypassages, in particular of coronary and peripheral arterial vessels,said catheter comprising a balloon having an interior through which aguide hose to be guided by a guide wire extends, said balloon includingan inflation tube opening into the interior of the balloon, wherein amicrowave antenna is located, said antenna coupled to a coaxial cable,the balloon including means for absorbing and/or shielding microwaveradiation, and further wherein the guide hose consists of a readilydeformable material and hence can be clamped off upon inflation of theballoon.
 2. A balloon catheter of claim 1 including a pressure sensormeans for generating a signal when the internal balloon pressure exceedsa predetermined threshold, whereby the microwave generator iscontrollable so as to be switched on only at sufficient pressure tosqueeze the guide hose flat.